Silent operating mode for reducing emissions of a hybrid electric vehicle

ABSTRACT

This novel silent operating mode for a hybrid electric vehicle (HEV) reduces noise and emissions compared to traditional HEV operating modes. It is a complementary series of software control functions that allows the vehicle to operate with reduced noise and emissions where specifically needed, while phasing-in engine power where allowed. The method utilizes an energy storage system budget associated with a modal quantity of energy allocated for the mode, and is adapted to automatically adjust the operation of the vehicle to accommodate deviations from the budgeted energy amount. The mode also adjusts the vehicle operation in conjunction with changes in the parametric conditions of the ESS.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is related to commonly assigned, co-pending U.S.patent application Ser. No. 10/686,015.

TECHNICAL FIELD

This invention generally comprises a method for implementing a silentmode of operating a hybrid electric vehicle (HEV) so as to reduce thenoise and exhaust emissions of the vehicle. More specifically, thesilent mode is a method of operating an HEV in a target area so as topreferentially use an electric drive motor driven by an energy storagesystem for vehicle propulsion rather than an engine, such as an internalcombustion engine. Most specifically, the silent mode is a method ofautomatically operating an HEV in a target area where an electric drivemotor driven by the energy storage system is designated as the primarysource of propulsion energy, and the engine is used only to make up abalance of the total propulsion energy demand that exceeds an energybudget of the electric drive motor/ESS.

BACKGROUND OF THE INVENTION

An HEV is a vehicle that has a propulsion system that consists of atleast one electric motor or electric machine in combination with atleast one other power source. Typically, the other power source is agasoline or diesel engine. There are various types of HEVs depending onhow the electric motor(s) and other power source(s) are combined withone another in order to provide propulsion for the vehicle, includingseries, parallel and compound HEVs.

Various hybrid powertrain architectures are known for managing the inputand output torques of various propulsion systems in HEVs, most commonlyinternal combustion engines and electric machines. Series hybridarchitectures are generally characterized by an internal combustionengine driving an electric generator which in turn provides electricalpower to an electric drivetrain and to an energy storage system,comprising a battery pack. The internal combustion engine in a seriesHEV is not directly mechanically coupled to the drivetrain. The electricgenerator may also operate in a motoring mode to provide a startingfunction to the internal combustion engine, and the electric drivetrainmay recapture vehicle braking energy by also operating in a generatormode to recharge the battery pack.

Parallel HEV architectures are generally characterized by an internalcombustion engine and an electric motor which both have a directmechanical coupling to the drivetrain. The drivetrain conventionallyincludes a shifting transmission to provide the necessary gear ratiosfor wide range operation.

Electrically variable transmissions (EVT) are known which provide forcontinuously variable speed ratios by combining features from bothseries and parallel HEV powertrain architectures. EVTs are operable witha direct mechanical path between an internal combustion engine and afinal drive unit thus enabling high transmission efficiency andapplication of lower cost and less massive motor hardware. EVTs are alsooperable with engine operation mechanically independent from the finaldrive or in various mechanical/electrical split contributions (i.e.input split, output split and compound split configurations) therebyenabling high-torque continuously variable speed ratios, electricallydominated launches, regenerative braking, engine off idling, andtwo-mode operation.

The development of new HEV powertrain architectures also facilitate thedevelopment and implementation of novel vehicle operating methodologiesthat utilize the novel features available in these systems. Newoperating methods are desired that utilize HEV powertrain architectures,for example, to provide vehicle operating methodologies that areparticularly adapted to their operating environments, or that meetlegal, regulatory or other constraints that are imposed upon theiroperating environments, such as by using novel combinations ofelectrical and mechanical propulsion energy to minimize vehicleemissions, such as noise and exhaust emissions. It is also desirablethat such operating methodologies are incorporated into the vehiclehardware and software systems as novel operating modes that areavailable for selection manually by an operator, or for automaticimplementation by the vehicle in response to predetermined conditions.

Complex EVT HEVs utilize one or more electric machines and requireadvanced, high energy density, energy storage systems (ESS) whichinclude batteries, ultracapacitors or combinations thereof, to supplyelectrical energy to and receive and store electrical energy from thesemachines. The implementation of new operating methodologies, placeincreased demands on the electric machines and ESS associated with thedynamic flow of power into and out of the ESS.

Therefore, it is highly desirable to develop vehicle operatingmethodologies that are adapted to vehicle operating environmentrequirements and that can be incorporated into the vehicles as operatingmodes that implement advance control of HEV systems, including theengine, electric machine and ESS systems.

SUMMARY OF THE INVENTION

The present invention is a method of providing a silent mode ofoperation for a hybrid electric vehicle having a rechargeable ESS. Themethod comprises a series of steps including: (1) transmitting a silentmode initiation request to a silent mode controller; (2) comparing anactual value of at least one state parameter of the ESS that isindicative of the availability of the ESS for implementing the silentmode to at least one silent mode initiation limit value associated withthe actual value, wherein if the actual value of at the least one stateparameter compared to the associated at least one mode initiation limitvalue indicates that the silent mode is allowed, the method proceeds tostep (3), and wherein if the actual value of the at least one stateparameter indicates that the silent mode is not allowed, step (2) isrepeated so long as the silent mode initiation request is beingtransmitted; (3) transmitting a silent mode activation request to thesilent mode controller;(4) operating the vehicle in the silent modeusing the silent mode controller, comprising designating an electricdrive motor as a primary source of propulsion energy for the vehicle anddesignating an engine as a secondary source of the propulsion energy forthe vehicle, wherein a modal quantity of energy in the ESS is allocatedfor use by the electric drive motor during the silent mode and theengine is used to make up the difference between the modal quantity ofenergy and a total vehicle propulsion energy requirement during thesilent mode; and (5) terminating the silent mode in response to theoccurrence of a mode termination event.

The method preferably includes a precharging step to establish a desiredmodal quantity of battery energy for use in implementing the method.

The method also preferably utilizes a battery budget to distribute themodal quantity of battery energy allocated for implementation of thesilent mode over the length of the target zone in which the mode is tobe implemented. The method also preferably utilizes a method ofcontrolling the battery budget using a battery budget factor, whichcompares the budgeted battery use with actual battery use in order todetermine when additional propulsion energy is required from the engine.

This method provides significant and readily appreciable advantages andbenefits associated with a substantial reduction of both noise andexhaust emissions within the target zone of its use.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be more fully understood from the detaileddescription given here below, the appended claims, and the accompanyingdrawings in which:

FIG. 1 is a mechanical hardware schematic representation of onepreferred form of a two-mode, compound-split, electrically variabletransmission particularly suited to the implementation of the presentinvention;

FIG. 2 is an electrical and mechanical schematic of a preferred systemarchitecture for the hybrid powertrain disclosed herein;

FIG. 3 is a graphical representation of various regions of operationwith respect to input and output speeds of the exemplary electricallyvariable transmission disclosed herein;

FIG. 4 is a block diagram illustrating steps of the method of thepresent invention;

FIG. 5 is a plot of battery usage as a function of distance traveled inthe target zone to illustrate a battery usage budget for the silent modeof the method the of present invention;

FIG. 6 is a plot of engine output power is a function of vehicle speedillustrating engine power usage in a target zone for the method of thepresent invention;

FIG. 7 is a plot of engine output power as a function of transmissionoutput speed and a battery budget factor for the method of the presentinvention.

FIG. 8 is a block diagram illustrating steps of the method of the stopmode of the present invention; and

FIG. 9 is a block diagram illustrating various states and transitions ofthe EVT powertrain associated with the stop mode of the method of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference first to FIGS. 1 and 2, a vehicular powertrain isgenerally designated 11. Included in the powertrain 11 is onerepresentative form of a multi-mode, compound-split, electricallyvariable transmission (EVT) particularly suited for implementing thecontrols of the present invention and designated generally by thenumeral 10 in FIGS. 1 and 2. With particular reference, then, to thosefigures, the EVT 10 has an input member 12 that may be in the nature ofa shaft which may be directly driven by an engine 14 or, as shown inFIG. 2, a transient torque damper 16 may be incorporated between theoutput member of the engine 14 and the input member of the EVT 10. Thetransient torque damper 16 may incorporate, or be employed inconjunction with, a torque transfer device (not shown) to permitselective engagement of the engine 14 with the EVT 10, but it must beunderstood that such a torque transfer device is not utilized to change,or control, the mode in which the EVT 10 operates.

In the embodiment depicted the engine 14 may be a fossil fuel engine,such as a diesel engine which is readily adapted to provide itsavailable power output delivered at a constant number of revolutions perminute (RPM). In the exemplary embodiment to which FIGS. 1 and 2 aredirected, the engine 14 can—after start-up, and during the majority ofits input—operate at a constant speed or at a variety of constant speedsin accordance with a desired operating point as may be determined fromoperator inputs and driving conditions.

The EVT 10 utilizes three planetary gear subsets 24, 26 and 28. Thefirst planetary gear subset 24 has an outer gear member 30, that maygenerally be designated as the ring gear, which circumscribes an innergear member 32, generally designated as the sun gear. A plurality ofplanet gear members 34 are rotatably mounted on a carrier 36 such thateach planet gear member 34 meshingly engages both the outer gear member30 and the inner gear member 32.

The second planetary gear subset 26 also has an outer gear member 38,generally designated as the ring gear, which circumscribes an inner gearmember 40, generally designated as the sun gear. A plurality of planetgear members 42 are rotatably mounted on a carrier 44 such that eachplanet gear 42 meshingly engages both the outer gear member 38 and theinner gear member 40.

The third planetary gear subset 28 also has an outer gear member 46,generally designated as the ring gear, which circumscribes an inner gearmember 48, generally designated as the sun gear. A plurality of planetgear members 50 are rotatably mounted on a carrier 52 such that eachplanet gear 50 meshingly engages both the outer gear member 46 and theinner gear member 48.

While all three planetary gear subsets 24, 26 and 28 are “simple”planetary gear subsets in their own right, the first and secondplanetary gear subsets 24 and 26 are compounded in that the inner gearmember 32 of the first planetary gear subset 24 is conjoined, as througha hub plate gear 54, to the outer gear member 38 of the second planetarygear subset 26. The conjoined inner gear member 32 of the firstplanetary gear subset 24 and the outer gear member 38 of the secondplanetary gear subset 26 are continuously connected to a firstmotor/generator 56, as by a sleeve shaft 58. First motor/generator 56may also be referred to herein variously as motor A or M_(A).

The planetary gear subsets 24 and 26 are further compounded in that thecarrier 36 of the first planetary gear subset 24 is conjoined, asthrough a shaft 60, to the carrier 44 of the second planetary gearsubset 26. As such, carriers 36 and 44 of the first and second planetarygear subsets 24 and 26, respectively, are conjoined. The shaft 60 isalso selectively connected to the carrier 52 of the third planetary gearsubset 28, as through a torque transfer device 62 which, as will behereinafter more fully explained, is employed to assist in the selectionof the operational modes of the EVT 10. Torque transfer device 62 mayalso be referred to herein variously as second clutch, clutch two or C2.

The carrier 32 of the third planetary gear subset 28 is connecteddirectly to the transmission output member 64. When the EVT 10 is usedin a land vehicle, the output member 64 may be connected to thevehicular axles (not shown) that may, in turn, terminate in the drivemembers (also not shown). The drive members may be either front or rearwheels of the vehicle on which they are employed, or they may be thedrive gear of a track vehicle.

The inner gear member 40 of the second planetary gear subset 26 isconnected to the inner gear member 48 of the third planetary gear subset28, as through a sleeve shaft 66 that circumscribes shaft 60. The outergear member 46 of the third planetary gear subset 28 is selectivelyconnected to ground, represented by the transmission housing 68, througha torque transfer device 70. Torque transfer device 70, as is alsohereinafter explained, is also employed to assist in the selection ofthe operational modes of the EVT 10. Torque transfer device 70 may alsobe referred to herein variously as first clutch, clutch one or C1.

The sleeve shaft 66 is also continuously connected to a secondmotor/generator 72. Second motor/generator 72 may also be referred toherein variously as motor B or M_(B). All the planetary gear subsets 24,26 and 28 as well as motor A and motor B (56, 72) are coaxiallyoriented, as about the axially disposed shaft 60. It should be notedthat both motors A and B are of an annular configuration which permitsthem to circumscribe the three planetary gear subsets 24, 26 and 28 suchthat the planetary gear subsets 24, 26 and 28 are disposed radiallyinwardly of the motors A and B. This configuration assures that theoverall envelope—i.e.: the circumferential dimension—of the EVT 10 isminimized.

A drive gear 80 may be presented from the input member 12. As depicted,the drive gear 80 fixedly connects the input member 12 to the outer gearmember 30 of the first planetary gear subset 24, and the drive gear 80,therefore, receives power from the engine 14 and/or the motor/generators56 and/or 72. The drive gear 80 meshingly engages an idler gear 82which, in turn, meshingly engages a transfer gear 84 that is secured toone end of a shaft 86. The other end of the shaft 86 may be secured to atransmission fluid pump and 88 which is supplied transmission fluid fromsump 37, delivering high pressure fluid to regulator 39 which returns aportion of the fluid to sump 37 and provides regulated line pressure inline 41.

In the described exemplary mechanical arrangement, the output member 64receives power through two distinct gear trains within the EVT 10. Afirst mode, or gear train, is selected when the first clutch C1 isactuated in order to “ground” the outer gear member 46 of the thirdplanetary gear subset 28. A second mode, or gear train, is selected whenthe first clutch C1 is released and the second clutch C2 issimultaneously actuated to connect the shaft 60 to the carrier 52 of thethird planetary gear subset 28.

Those skilled in the art will appreciate that the EVT 10 is capable ofproviding a range of output speeds from relatively slow to relativelyfast within each mode of operation. This combination of two modes with aslow to fast output speed range in each mode allows the EVT 10 to propela vehicle from a stationary condition to highway speeds. In addition, afixed-ratio state wherein both clutches C1 and C2 are simultaneouslyapplied is available for efficient mechanical coupling of the inputmember to the output member through a fixed gear ratio. Furthermore, aneutral state wherein both clutches C1 and C2 are simultaneouslyreleased is available for mechanically decoupling the output member fromthe transmission. Finally, the EVT 10 is capable to provide synchronizedshifts between the modes wherein slip speed across both clutches C1 andC2 is substantially zero. Additional details regarding operation of theexemplary EVT can be found in commonly assigned U.S. Pat. No. 5,931,757,the contents of which are incorporated herein by reference.

Engine 14 is preferably a diesel engine and electronically controlled byengine control module (with the) 23 as illustrated in FIG. 2. ECM 23 isa conventional microprocessor based diesel engine controller comprisingsuch common elements as microprocessor, read only memory ROM, randomaccess memory RAM, electrically programmable read only memory EPROM,high speed clock, analog to digital (A/D) and digital to analog (D/A)circuitry, and input/output circuitry and devices (I/O) and appropriatesignal conditioning and buffer circuitry. ECM 23 functions to acquiredata from a variety of sensors and control a variety of actuators,respectively, of the engine 14 over a plurality of discrete lines. Forsimplicity, ECM 23 is shown generally in bi-directional interface withengine 14 via aggregate line 35. Among the various parameters that maybe sensed by ECM 23 are oil sump and engine coolant temperatures, enginespeed (Ne), turbo pressure, and ambient air temperature and pressure.Various actuators that may be controlled by the ECM 23 include fuelinjectors, fan controllers, engine preheaters including glow plugs andgrid-type intake air heaters. ECM preferably provides for well knowntorque based controls for engine 14 in response to a torque commandTe_cmd provided by the EVT control system. Such engines electronics,controls and quantities are generally well known to those skilled in theart and further detailed exposition thereof is not required herein

As should be apparent from the foregoing description the EVT 10selectively receives power from the engine 14. As will now be explainedwith continued reference to FIG. 2 the EVT also receives power from anelectric energy storage device or system 20 (ESS), such as one or morebatteries in battery pack module (BPM) 21. As used herein, reference toa battery includes not only a single battery, also includes anycombination of single or multiple batteries, or cells thereof, into abattery pack or array, or a plurality of battery packs or arrays. BPM 21is preferably a parallel array of battery packs, each of which comprisesa plurality of batteries. As used herein, the term battery generallyrefers to any secondary or rechargeable battery, but those comprisinglead/acid, nickel/metal hydride (Ni/NMH), or Li/ion or polymer cells arepreferred. Other electric energy storage devices that have the abilityto store electric power through charging and dispense electric powerthrough discharging, such as super capacitors or ultracapacitors, may beused in place of, or in combination with, the batteries without alteringthe concepts of the present invention. The BPM 21 is high voltage DC(e.g., about 650 V in an exemplary embodiment) coupled to dual powerinverter module (DPIM) 19 via DC lines 27. Current is transferable to orfrom the BPM 21 in accordance with whether the BPM 21 is being chargedor discharged. BPM 21 also comprises a conventional microprocessor basedcontroller comprising such common elements as microprocessor, read onlymemory ROM, random access memory RAM, electrically programmable readonly memory EPROM, high speed clock, analog to digital (A/D) and digitalto analog (D/A) circuitry, and input/output circuitry and devices (I/O),temperature sensors and appropriate signal conditioning and buffercircuitry necessary to monitor the state of the battery and transmitthis information to other portions of the control system for use in theoverall control of the vehicle, such as VCM 15 and TCM 17. This includessensing, processing, calculating and otherwise monitoring variousparametric information regarding the state or condition of the battery,such as its temperature, current and voltage while charging anddischarging, and state of charge (SOC), which comprises theinstantaneous amount of energy stored in the battery expressed as apercentage of its total energy storage capacity. This also includes is atransmitting the information concerning these parameters to otherportions of the vehicle control system, including the VCM 15 and TCM 17,for use in conjunction with control algorithms which make use of batteryparametric information, such as those used to establish SOC-relatedcharge and discharge limits, amp-hour/hour or energy throughput limits,temperature limits or other battery-related control functions.

DPIM 19 includes a pair of power inverters and respective motorcontrollers configured to receive motor control commands and controlinverter states therefrom for providing motor drive or regenerationfunctionality. Motor controllers are microprocessor based controllerscomprising such common elements as microprocessor, read only memory ROM,random access memory RAM, electrically programmable read only memoryEPROM, high speed clock, analog to digital (A/D) and digital to analog(D/A) circuitry, and input/output circuitry and devices (I/O) andappropriate signal conditioning and buffer circuitry. In motoringcontrol, the respective inverter receives current from the DC lines andprovides AC current to the respective motor over high voltage phaselines 29 and 31. In regeneration control, the respective inverterreceives AC current from the motor over high voltage phase lines 29 and3 land provides current to the DC lines 27. The net DC current providedto or from the inverters determines the charge or discharge operatingmode of the BPM 21. Preferably, M_(A) and M_(B) are three-phase ACmachines and the inverters comprise complementary three-phase powerelectronics. Individual motor speed signals Na and Nb for M_(A) andM_(B), respectively, are also derived by the DPIM 19 from the motorphase information or in conventional rotation sensors. Such motors,electronics, controls and quantities are generally well known to thoseskilled in the art and further detailed exposition thereof is notrequired herein.

System controller 43 is a microprocessor based controller comprisingsuch common elements as microprocessor, read only memory ROM, randomaccess memory RAM, electrically programmable read only memory EPROM,high speed clock, analog to digital (A/D) and digital to analog (D/A)circuitry, digital signal processor (DSP), and input/output circuitryand devices (I/O) and appropriate signal conditioning and buffercircuitry. In the exemplary embodiment, system controller 43 comprises apair of microprocessor based controllers designated as vehicle controlmodule (VCM) 15 and transmission control module (TCM) 17. VCM and TCMmay provide, for example, a variety of control and diagnostic functionsrelated to EVT and vehicle chassis including, for example, engine torquecommands, input speed control, and output torque control in coordinationwith regenerative braking, anti-lock braking and traction control.Particularly with respect to EVT functionality, system controller 43functions to directly acquire data from a variety of sensors anddirectly control a variety of actuators, respectively, of the EVT over aplurality of discrete lines. For simplicity, system controller 43 isshown generally in bi-directional interface with EVT via aggregate line33. Of particular note, system controller 43 receives frequency signalsfrom rotation sensors for processing into input member 12 speed Ni andoutput member 64 speed No for use in the control of EVT 10. Systemcontroller 43 may also receive and process pressure signals frompressure switches (not separately illustrated) for monitoring clutch C1and C2 application chamber pressures. Alternatively, pressuretransducers for wide range pressure monitoring may be employed. PWMand/or binary control signals are provided by system controller to EVT10 for controlling fill and drain of clutches C1 and C2 for applicationand release thereof. Additionally, system controller 43 may receivetransmission fluid sump 37 temperature data, such as from conventionalthermocouple input (not separately illustrated) to derive sumptemperature Ts and provide a PWM signal which may be derived from inputspeed Ni and sump temperature Ts for control of line pressure viaregulator 39. Fill and drain of clutches C1 and C2 are effectuated byway of solenoid controlled spool valves responsive to PWM and binarycontrol signals as alluded to above. Similarly, line pressure regulator39 may be of a solenoid controlled variety for establishing regulatedline pressure in accordance with the described PWM signal. Such linepressure controls are generally well known to those skilled in the art.Clutch slip speeds across clutches C1 and C2 are derived from outputspeed No, M_(A) speed Na and M_(B) speed Nb; specifically, C1 slip is afunction of No and Nb, whereas C2 slip is a function of No, Na and Nb.Also illustrated is user interface (UI) block 13 which comprises suchinputs to system controller 43 such as vehicle throttle position, pushbutton shift selector (PBSS) for available drive range selection, brakeeffort and fast idle requests among others. System controller 43determines a torque command Te_cmd and provides it to ECM 23. Torquecommand Te_cmd is representative of the EVT torque contribution desiredfrom the engine as determined by the system controller.

The various modules described (i.e. system controller 43, DPIM 19, BPM21, ECM 23) communicate via controller area network (CAN) bus 25. TheCAN bus 25 allows for communication of control parameters and commandsbetween the various modules. The specific communication protocolutilized will be application specific. For example the preferredprotocol for heavy duty applications is the Society of AutomotiveEngineers standard J1939. The CAN bus and appropriate protocols providefor robust messaging and multi-controller interfacing between the systemcontroller, ECM, DPIM, BPIM and other controllers such as antilock brakeand traction controllers.

With reference to FIG. 3, a plot of output speed No along the horizontalaxis versus input speed Ni across the vertical axis for the EVT 10 isillustrated. Synchronous operation, that is the input speed and outputspeed relationships whereat both clutch C1 and C2 are operatingsimultaneously with substantially zero slip speed thereacross isrepresented by line 91. As such, it represents the input and outputspeed relationships substantially whereat synchronous shifting frombetween modes can occur or whereat direct mechanical coupling from inputto output can be effected by simultaneous application of both clutchesC1 and C2, also known as fixed-ratio. One particular gearsetrelationship capable of producing the synchronous operation depicted byline 91 in FIG. 3 is as follows: outer gear member 30 having 91 teeth,inner gear member 32 having 49 teeth, planet gear members 34 having 21teeth; outer gear member 38 having 91 teeth, inner gear member 40 having49 teeth, planet gear members 42 having 21 teeth; outer gear member 46having 89 teeth, inner gear member 48 having 31 teeth, planet gearmembers 50 having 29 teeth. Line 91 may be variously referred to hereinas synchronous line, shift ratio line or fixed-ratio line.

To the left of the shift ratio line 91 is a preferred region ofoperation 93 for the first mode wherein C1 is applied and C2 isreleased. To the right of the shift ratio line 91 is a preferred regionof operation 95 for the second mode wherein C1 is released and C2 isapplied. When used herein with respect to clutches C1 and C2, the termapplied indicates substantial torque transfer capacity across therespective clutch while the term released indicates insubstantial torquetransfer capacity across the respective clutch. Since it is generallypreferred to cause shifts from one mode to the other to occursynchronously, torque transfers from one mode into the other mode arecaused to occur through a two clutch application fixed ratio wherein,for a finite period prior to the release of the presently appliedclutch, the presently released clutch is applied. And, the mode changeis completed when fixed-ratio is exited by the continued application ofthe clutch associated with the mode being entered and the release of theclutch associated with the mode being exited. While region of operation93 is generally preferred for the operation of the EVT in MODE 1, it isnot meant to imply that MODE 2 operation of the EVT cannot or does notoccur therein. Generally, however, it is preferred to operate in MODE 1in region 93 because MODE 1 preferably employs gearsets and motorhardware particularly well suited in various aspects (e.g. mass, size,cost, inertial capabilities, etc.) to the high launch torques of region93. Similarly, while region of operation 95 is generally preferred forthe operation of the EVT in MODE 2, it is not meant to imply that MODE 1operation of the EVT cannot or does not occur therein. Generally,however, it is preferred to operate in MODE 2 in region 95 because MODE2 preferably employs gearsets and motor hardware particularly wellsuited in various aspects (e.g. mass, size, cost, inertial capabilities,etc.) to the high speeds of region 93. A shift into MODE 1 is considereda downshift and is associated with a higher gear ratio in accordancewith the relationship of Ni/No. Likewise, a shift into MODE 2 isconsidered an upshift and is associated with a lower gear ratio inaccordance with the relationship of Ni/No.

The present invention comprises a method 100 for implementing a silentmode 110 or HUSH mode 110 of operating an HEV 115, such as one havingpowertrain 11, so as to reduce noise and exhaust emissions compared tonormal HEV operating modes. While the present invention is particularlysuited for use in an HEV 115 having EVT powertrain 11, it is alsobelieved to be applicable to many other series, parallel and EVT HEVpowertrain configurations, including single, double or multimode, input,output or compound split EVT configurations. The method preferably isimplemented as a complementary series of software control functions orinstructions in a silent mode controller 125 such as VCM15, TCM 17, orone of the other controllers described above, that allow the vehicle tooperate with reduced noise and emissions where specifically needed,while phasing-in engine power as necessary and subject to certainconstraints. Applicants have implemented elements of method 100 in bothVCM 15 and TCM 17, but it is believed that method 100 may also beimplemented in other control modules or controllers within the vehiclein accordance with system design and other considerations.

Silent mode 110 is particularly applicable for use in an REV comprisinga transit bus having an EVT powertrain operating in a tunnel or otherenclosed space, such as a parking garage or large building, with aplurality of passenger or other stops. Other applications could includetransit buses, garbage trucks or other delivery vehicles operating (withpick-ups and drop-offs) in a noise or exhaust emission restricted region(e.g., hospital zones and certain neighborhoods). Method 100 isapplicable over well-defined routes as well as undefined routes within adefined region, and may also be applicable for use where neither a routenor region is predefined, but wherein a location or region is adapted tocommunicate that silent mode operation is desired to a vehicle that isadapted to receive such communication and implement method 100. As usedherein, a “target zone” refers to a location, area or region in which itis desired or intended that the vehicle operates in silent mode 110 soas to effect reduced noise and exhaust emissions.

Referring to FIG. 4, the present invention may be described generally asa method 100 of providing a silent mode 110 of operation for an HEV 115having a rechargeable energy storage system 20 (ESS), comprising thesteps of: (1) transmitting 200 a silent mode initiation request 120 to asilent mode controller 125; (2) comparing 300 an actual value of atleast one state parameter 130 of ESS 20 that is indicative of theavailability of ESS 20 for implementing silent mode 110 to at least onesilent mode initiation limit value 135 associated with the actual value130, wherein if the actual value of the at least one state parameter 130compared to the associated at least one mode initiation limit value 135indicates that silent mode 110 is allowed, method 100 proceeds to step(3), and wherein if the actual value of the at least one state parameter130 indicates that silent mode 110 is not allowed, step (2) is repeatedso long as silent mode initiation request 120 is being transmitted; (3)transmitting 400 silent mode activation request 140 to silent modecontroller 125; and (4) operating 500 the vehicle in silent mode 110using silent mode controller 125, comprising designating electric drivemotor 143 as a primary source of propulsion energy for the vehicle anddesignating engine 145 as a secondary source of the propulsion energyfor the vehicle, wherein a modal quantity 150 of energy in ESS 20 isallocated for use by electric drive motor 143 during silent mode 110 andengine 145 is used to make up the difference between the modal quantityof energy 150 and a total vehicle propulsion energy requirement 155during silent mode 110; and (4) terminating 500 silent mode 110 inresponse to the occurrence of mode termination event 160. These stepsare described further below.

The first step of method 100 comprises transmitting 200 silent modeinitiation request 120 to silent mode controller 125. Silent modeinitiation request 120 may be transmitted by any suitable means, such asmanual transmitting 200 of silent mode initiation request 120 by avehicle operator, automatic transmitting 200 of silent mode initiationrequest 120 as a function of an absolute position of the vehicle, andautomatic transmitting 200 of silent mode initiation request 120 as afunction of a relative position of the vehicle to a region in whichsilent mode operation of the vehicle is desired. Manual transmitting 200of silent mode initiation request 120 by a vehicle operator may be doneby actuation of a switch, or making an appropriate selection from a userinterface or graphic user interface, such as user interface (UI) 13 (seeFIG. 1), that is in signal communication with silent mode controller125. The transmitting 200 of silent mode initiation request 120 may alsobe coupled to a suitable feedback indicator and associatedimplementation mechanism in order to provided an indication to theoperator that the request has been made or is being processed by silentmode controller 125, such as incorporating an indicator light into orassociated with the manual mode selector means, such as a lightedswitch, or a display on UI 13 which indicates that mode initiationrequest 120 has been made or is being processed. Automatic transmitting200 of the silent mode initiation request 120 as a function of anabsolute position of the vehicle may be accomplished, for example, byautomatically and continuously comparing an input signal that isindicative of the actual latitude and longitude position of the vehicle,such as a signal received from a global positioning satellite (GPS),with a set of latitude and longitude coordinates that identify a targetzone or target zones, wherein a request for silent mode 110 operation isautomatically transmitted 200 as an input signal to silent modecontroller 125 if the comparison indicates that the vehicle is in atarget zone. Such GPS signals may be monitored by GPS systems that areadapted to automatically and continuously receive such signals andprovide an output signal indicative of an absolute latitude/longitudeposition of the vehicle which are known in the art, and such outputsignals may be automatically and continuously provided to silent modecontroller 125. Automatic transmitting of the silent mode initiationrequest as a function of a relative position of the vehicle to a regionin which silent mode operation of the vehicle is desired may beaccomplished, for example, by incorporation of proximity sensors on thevehicle that are adapted to sense a signal associated with and proximateto a target zone. This could include, for example, use of an FM receiveron the vehicle that is adapted to receive an FM signal from atransmitter associated with a target zone, wherein the FM signal isindicative of the proximity of the vehicle to the target zone.

Referring again to FIG. 4, method 100 continues with the step ofcomparing 300 an actual value of at least one state parameter 130 of ESS20 that is indicative of the availability of ESS 20 for implementingsilent mode 110 to at least one silent mode initiation limit value 135associated with the actual value 130, wherein if the actual value of theat least one state parameter 130 compared to the associated at least onemode initiation limit value 135 indicates that silent mode 110 isallowed, method 100 proceeds to the next step, and wherein if the actualvalue of the at least one state parameter 130 indicates that silent mode110 is not allowed, this test is repeated so long as silent modeinitiation request 120 is being transmitted to silent mode controller125. As described above, state parameters of the ESS, such as battery orBPM 21, may comprise any parameters that are indicative of theavailability of the ESS for use generally, and particularly for use inconjunction with implementation of silent mode 110, including parametersthat provide information about either the short-term or long-termcharacteristics or condition of the ESS. These include the instantaneousbattery temperature (T_(BAT)), the battery SOC and the average amp-hourper hour throughput of the battery (AH/H). The T_(BAT) is an importantparameter because both charging and discharging of the battery increasethe battery temperature (e.g. Under most conditions charging has thegreater effect on temperature, but discharging also increases thebattery temperature). As the battery temperature increases, the chargingand discharging efficiency and the ability to obtain and maintain adesired SOC is affected. Further, overheating of the battery can alsoreduce its service life and available total amp-hour/hour throughput.The battery SOC is an important parameter because it provides animportant indication of the total energy available in the battery, andits ability to provide charge to or accept charge from DPIM 19 and theother components of EVT 11. SOC is also important because high and lowSOC conditions are associated with overvoltage and undervoltageconditions, respectively, both of which can damage the battery andreduce its service life. The integrated amp-hour/hour throughput is animportant parameter because it is known to be directly related to theoperational service life of the battery. The amp-hour per hourthroughput of the ESS may be measured by integrating the ESS currentover time using a predetermined filter and algorithm. Further detailsregarding amp-hour per hour throughput can be found in commonlyassigned, co-pending U.S. provisional patent application Ser. No.60/511,456, which is hereby incorporated herein by reference in itsentirety. In a preferred embodiment, this step comprises comparing 300T_(BAT) to a silent mode initiation battery temperature limit value 135,wherein if T_(BAT) is less than the mode initiation battery temperaturelimit value (T_(SMI)), the method proceeds to step (3), and wherein ifT_(BAT)≧T_(SMI), this step is repeated so long as silent mode initiationrequest 120 is being transmitted.

Where ESS comprises a battery, if T_(BAT)≦T_(SMI), method 100 preferablyalso comprises a step (2A) of precharging 350 the battery 21 prior toinitiation of silent mode 110. This is preferred in order to ensure thatbattery 21 has an SOC that is sufficient to supply the quantity ofelectrical energy necessary to implement method 100, as describedherein. It is also preferred when precharging 350 that this step belimited to precharging the ESS to a state of charge (SOC) value that isless than or equal to a target precharge SOC limit 165. The purpose ofthis SOC precharging limit is to limit the temperature increase in thebattery associated with charging. Another purpose of the upperprecharging SOC limit is to make for consistent charge times and toensure that enough energy is in the ESS white not unnecessarilyincreasing the AH/H throughput or SOC swing of the ESS by driving theSOC higher than necessary to travel the target distance. There are alsolife considerations with how much and how quickly the SOC swings fromminimum to maximum. One purpose behind the maximum SOC precharge limitis to keep the SOC high enough that if the silent mode uses the entireallocated budget, the minimum limit would not be exceeded. Becauseprecharging 350 is done in anticipation of an immediate and possiblyextended discharge from battery as silent mode 110 is initiated, andbecause discharge also causes additional heating of the battery, it ispreferred that precharging be limited to an SOC that is less than orequal to target precharge SOC limit 165. The target precharge SOC limit165 will necessarily vary depending on the capacity, construction andconfiguration of battery 21 and other system design factors such themaximum battery power requirements associated with projected vehicleloads, target zone parameters and other factors, and may be expressed asa target value, minimum/maximum value or other similar method ofidentifying a limit value. For example, in one embodiment associatedwith BPM 21, where the length of the target zone was about 2.2 km. andthe battery had a total capacity (SOC_(100%)) of about 19 amp-hours, thetarget precharge SOC limit 165 was about 60%, or 11.4 amp-hours. Whenthe SOC of battery 21 reaches target precharge SOC limit 165,precharging 350 is complete and silent mode controller 125 stopsprecharging 350. Precharging 350 is also preferably terminated if silentmode 110 is initiated prior to the battery SOC reaching target prechargeSOC limit 165. It is preferred that precharging 350 comprises chargingESS 20 at a maximum charging power of the vehicle consistent withcontrol of parametric ESS limits associated with ESS charge/discharge,SOC and temperature, such as those described in commonly assigned,co-pending U.S. patent application Ser. No. 60/511,456. Further, duringprecharging 350 the vehicle is adapted to operate engine 145 at acombination of Ni and Ti that maximizes the charging power available tothe ESS and which are generally consistent with other systemrequirements, such as the desired No and To. However, the step ofprecharging 350 may be adapted to select combinations of Ni and Ti thatpreferentially maximize the charge power to the ESS, even though suchchoices may constrain the possible values of No and To to values thatare less than desired or commanded values. The method of determiningcombinations of Ni and Ti to affect the desired control of the EVTpowertrain are described in commonly assigned, co-pending U.S. patentapplication Ser. Nos. 10/686,508 and 10/686,034, which are herebyincorporated herein by reference in their entirety. When the desiredtarget precharge SOC is reached during precharging 350, charging ispreferably stopped and is not resumed unless vehicle operation requiresa discharge that causes the SOC to drop below the target precharge SOC.Precharging 350 may also be scheduled for a particular duration of time,subject to parametric limits as described herein. The step ofprecharging 350 is preferred, but optional and not essential to thepractice of method 100, since ESS 20 may comprise more than battery 21,as explained above, and because even when ESS consists of a battery, thecontrol algorithms concerning SOC may be such that precharging 350 isnot required prior to implementing method, such as HEVs in which otherconstraints require that the SOC always be maintained at a level that issufficient to implement silent mode 110 without the need forprecharging.

Referring to FIG. 4, following the steps of comparing 300 and anyprecharging 350, method 100 proceeds with the step (3) of transmitting400 silent mode activation request 140 using silent mode controller 125.Transmitting 400 may be accomplished in a manner analogous to the stepof transmitting 200, in that silent mode 110 may be activated bytransmitting 400 silent mode activation request 140 to silent modecontroller 125 by any suitable means, such as manually transmitting 400silent mode activation request 140 by a vehicle operator, automaticallytransmitting 400 silent mode activation request 140 as a function of anabsolute position of the vehicle, and automatically transmitting 400silent mode activation request 140 as a function of a position of thevehicle relative to a region in which silent mode operation of thevehicle is desired. Transmitting 400 of silent mode activation request140 may also be accomplished as a function of elapsed time or distanceafter transmitting 200 of silent mode initiation request 120, orinitiation or completion of precharging 350.

Referring to FIG. 4, following the steps of transmitting 400 of silentmode activation request 140, method 100 proceeds with step (4) ofoperating 500 the vehicle in silent mode 110 using silent modecontroller 125, comprising designating an electric drive motor 143, suchas motor A (56) or motor B (72), as a primary source of propulsionenergy for the vehicle and designating an engine 145, such as engine 14,as a secondary source of the propulsion energy for the vehicle, whereina modal quantity 150 of energy in ESS 20 is allocated for use byelectric drive motor 143 during silent mode 110 and engine 145 is usedto make up the difference between modal quantity of energy 150 and thetotal vehicle propulsion energy 155 requirement during silent mode 110.Engine 145 is secondary in that it is only used in order to make up thedifference between modal quantity of energy 150 and the total vehiclepropulsion energy 155 requirement during silent mode 110, and if modalquantity 150 is sufficient, engine 145 is preferably not fueled androtated by electric drive motor 143, such as motor A (56) or motor B(72). If engine 145 is required, it is only fueled so as to provide thenecessary propulsion energy differential, rather than, for example, atits maximum rated capacity. This is illustrated in FIG. 6, which plotsengine 145 output power as a function of vehicle speed for a particularpoint of consumption of the SOC allocated for silent mode 110 forillustration of an exemplary implementation of method 100. At a vehiclespeeds below about 17 mph, there is no output power or energycontribution from engine 145. At vehicle speeds from 17 mph to about 24mph, the propulsion energy contribution of engine 145 is increased at aconstant rate to a maximum silent mode value at vehicle speeds aboveabout 24 mph. The maximum engine output power while the vehicle is insilent mode 110 is limited to a maximum silent mode output power limit175 that is preferably selected to be less than a maximum output power180 of engine 145 in order to reduce noise and exhaust emissions in thetarget zone. A modal quantity 150 of energy in the ESS 20 is allocatedfor use during silent mode 110. Modal quantity 150 may comprise anyportion of the available SOC of the battery. However, in order tosimplify implementation of method 100, it is preferred that the portionof the SOC allocated as modal quantity 150 comprise a fixed portion orpercentage of the maximum SOC, or maximum energy storage capacity ofbattery 21. For example, in the case of a battery 21 having a maximumenergy storage capacity of 19 amp-hours, modal quantity 150 of batteryenergy comprised 4.75 amp-hours, or about 25% of the maximum SOC.However, if precharging 350 does not provide the desired targetprecharge SOC value, or if the actual SOC level at exceeds the targetprecharge SOC, method 100 may adapt modal quantity 150 of energy toadjust for the deficit or surplus, as further described herein.

Modal quantity 150 of energy may be allocated for use during silent mode110 according to any suitable allocation scheme, but a preferred schemeis to establish or calculate an ESS usage budget 185 for use duringsilent mode 110, such as the one shown in FIG. 5, wherein modal quantity150 of battery energy is normalized and allocated as a function of thetotal distance traveled, or length of the target zone. The budget may belinear or non-linear depending on variations associated with target zonealong its length (e.g., extended stops, grade variations, etc.) vehicleload and other factors.

As the vehicle travels through the target zone, the actual usage ofmodal quantity 150 of battery energy deviates from the ESS usage budget.When deviations occur such that actual usage of modal quantity 150 ofESS propulsion energy is greater than the budgeted amount, engine 145 isused to supply the difference. The amount of engine output powernecessary may be calculated as a function of vehicle speed and aspeed/charge consumption dependent ESS budget factor (EBF) 190. EBF 190provides an indication of how much the amount of ESS energy actuallyconsumed as a function of distance in the target zone has deviated fromthe ESS usage budget established for modal quantity of energy 150associated with that distance. The EBF 190 is calculated as:

${EBF} = {1 - \frac{\left( {{\Delta\;{SOC}_{INSTANT}} - {\Delta\;{SOC}_{BUDGET}}} \right)}{K}}$where:ΔSOC _(INSTANT) =SOC _(INITIAL) −SOC _(INSTANT)ΔSOC _(BUDGET) =SOC _(BUDGET) −SOC _(INSTANT)and

-   -   SOC_(BUDGET)=the amount of SOC_(100%) budgeted for use during        the silent mode as a function of distance, in percent;    -   SOC_(INITIAL)=the SOC at the initiation of the silent mode, in        percent;    -   SOC_(INSTANT)=the instantaneous SOC as a function of distance,        in percent;    -   SOC_(100%)=the total charge capacity of the battery; and    -   K=a constant for a given EVT powertrain, similar to a gain, and        in an EVT 11 HEV, the value of K was preferably about 5.

FIG. 7 illustrates a plot of engine output power as a function of EBF190 and the transmission output speed in revolutions per minute, whichis directly related to the vehicle speed. In the illustrated embodiment,the transmission output speed (rpm) was related to vehicle speed (mph)by multiplying transmission output speed by a factor of 0.022. Thisrelationship may be stored in a lookup table. The axes representboundary conditions. At transmission output speeds above 1364 rpm, motoroutput power is constant as a function of vehicle speed and varies onlymodestly as a function of the battery budget factor 190. The batterybudget factor is limited to 0 for values that are less than zero and 1for values that are greater than 1. For negative vehicle speeds, theoutput power was limited to the values associated with zero vehiclespeed The value of EBF 190 may be calculated by silent mode controller125 and vehicle output speed may be obtained from, for example, TCM 17.These may be used to look up the engine output power necessary to makeup any differences between the budgeted amount of modal quantity 150 ofenergy allocated for propulsion of the vehicle and the total vehiclepropulsion energy requirement. The engine output power from the look uptable is used by VCM 15 to affect control of engine 145 and supply thedifference between the ESS budget amount and the total vehiclepropulsion requirement based on the EBF.

As noted above, if the actual precharge SOC deviates from the targetprecharge SOC, either higher or lower, the ESS budget is preferablyadjusted using a ESS budget adjustment factor (EBAF), which may bedeveloped empirically or theoretically based upon the target prechargeSOC and its desired design limits. In an exemplary embodiment, where thetarget precharge SOC was 60% and the modal quantity 150 was 25% of themaximum SOC, the EBAF was calculated as shown below:

${EBAF} = \frac{{SOC}_{INITIAL} - 30}{25}$where EBAF was constrained to values in the range. 0.1≦EBAF≦1. Thebattery budget was multiplied by the EBAF to adjust the battery budgetfor deviations of SOC_(INITAL) from the target precharge SOC.

Referring to FIG. 4, following the step of operating 500 the vehicle insilent mode 110, method 100 proceeds with step (4) comprisingterminating 600 silent mode 110 in response to the occurrence of modetermination event 160. There are a plurality of mode termination eventsthat may be selected from the group consisting of: (a) manualtransmitting of a silent mode termination request by a vehicle operator,(b) automatic transmitting of a silent mode termination request as afunction of the absolute position of the vehicle, (c) automatictransmitting of a silent mode termination request as a function of arelative position of the vehicle to a region in which silent modeoperation of the vehicle is desired a manual mode termination command,(d) reaching a predetermined silent mode elapsed time limit, (e)reaching a predetermined silent mode elapsed distance limit, and (f)reaching at least one ESS state parameter termination limit. Modetermination events (a)–(c) are analogous to the corresponding eventsdescribed above associated with transmitting mode initiation and modeactivation requests, except that they are associated with exiting,rather than entering, a target zone, and may be performed in the mannerdescribed therein. Mode termination events (d) and (e) are particularlyadapted for use when either an elapsed distance within the target zoneor an elapsed time within target zone is known or can be characterizedsufficiently such that an elapsed mode distance limit or an elapsed modetime limit, respectively, can be established for automatic terminationof silent mode 110. The actual elapsed mode distance can be determinedfor comparison against the elapsed mode distance limit by measuring anodometer signal when silent mode 110 is initiated and periodicallycomparing it with an instantaneous odometer value in order to develop anactual elapsed mode distance value. Similarly, the actual elapsed modetime can be determined for comparison against the elapsed mode timelimit by initiating a timer when silent mode 110 is initiated andperiodically comparing the initial value with an instantaneous timervalue in order to develop an actual elapsed mode time value. Modetermination events (f) comprises reaching at least one ESS stateparameter termination limit. As described above, in the case where ESScomprises a battery, the state parameter may comprise a maximum batterytemperature limit, wherein reaching the maximum limit temperaturetriggers the termination of silent mode. The limit temperature should beselected so as to protect the battery from conditions that could causeshort term or long term damage. For example, in an embodiment where theESS comprised a NiMH battery, a limit of 50° C. was selected. Similarly,in the case where ESS comprises a battery, the state parameter maycomprise a minimum battery SOC limit, maximum battery SOC limit, orboth, wherein reaching the limit SOC triggers the termination of silentmode. For example, in an embodiment comprising a NiMH battery,minimum/maximum SOC limits of 20%≧SOC≧90 were selected.

Referring to FIGS. 6 and 7, the maximum silent mode output power limitof engine 145 is automatically controlled as a function of vehiclespeed. As vehicle speeds approach zero, the maximum silent mode outputpower of engine 175 is gradually reduced, until at relatively lowvehicle speeds that are less than a vehicle stop threshold value 710,but greater than zero, the maximum silent mode engine output power 175becomes zero, except for very low values of the battery budget factor(i.e., situations where the consumption of the battery charge issignificantly ahead of the budgeted amount). The maximum silent modeengine output power 175 may be reduced by gradually defueling (graduallyreducing the amount of fuel supplied per unit of time) engine 145. Asthe amount of fuel is reduced, engine 145, the maximum silent modeengine output power 175 is also reduced, until at the vehicle stopthreshold value 710, the fueling is stopped altogether and the maximumsilent mode engine output power 175 becomes zero. For example, referringto FIG. 6, when EBF=1 (i.e., actual power consumption equals thebudgeted amount), vehicle stop threshold value 710 is about 17 mph. Eventhough fueling is stopped at vehicle stop threshold value 710, engine145 is preferably rotated by one of the at least one electric drivemotors 143. Rotation of the engine and members which are coupled to itimproves the responsiveness of the overall EVT powertrain to enginerestart requests and also permits common mechanical and/or hydraulicsubsystems, such as transmission lubrication systems, to be powered evenwhile the output power of the engine is zero without the need forexpensive reengineering to provide their functionality while the engineis not rotating.

It is preferred that silent mode I 10 also be adapted to detect andrespond to changes in the grade of the route over which vehicle isoperated while it is in silent mode 110, because an increased grade maycause significant deviations from the battery budget and effectperformance in the mode because it results in slow vehicle speeds whichmay not otherwise call for any, or for increased engine output power.For a given vehicle, parametric limit values of output torque (To),output speed (No) and vehicle acceleration (No_dot) can be developedthat are indicative of the grade of the route and its slope, which maybe described generally as ranges of high output torque, slow or slowingvehicle speed and low or slowing acceleration. Parametric limits inthese values may be established, and incorporated into the silent modecontroller such as by the use of a look up table or tables. Applicantshave determined that upon detection of a grade that exceeds parametriclimits, electric-only propulsion power may not enough to accelerate thevehicle up a grade, and that it is desirable to command an engine outputpower (e.g., 100 kW) under such conditions that will insure that thetotal vehicle propulsion energy is sufficient, and which will alsoensure that vehicle is operating in a range of output power wherein thesilent mode control algorithm is effective to maintain proper control inview of the silent mode battery budget, and wherein the battery budgetfactor provides an accurate indication of the required output power as afunction of vehicle speed.

Method 100 also preferably comprises an automatic engine stop/restartand range select method 700, referred to herein as engine stop mode 710,which may be incorporated into and used in conjunction with silent mode110. Method 700 allows the engine to shut down automatically when thevehicle is stopped loading and unloading passengers. This featurereduces the noise and emissions of the vehicle when stopped, which notonly benefits the passengers on the bus, but also benefits the operatorsand by-standers near the bus. Engine stop mode 710 is particularlyadvantageous in that it makes the most significant reductions in noiseand exhaust emissions at the points that they are most noticeable tooperators, passengers and bystanders, namely the points at which thevehicle stops, such as pick-up and drop-off points.

To enhance the benefit of reductions in noise and exhaust emissions atpickup and drop-off points, it is also desirable to affect substantiallyreduced noise and exhaust emission control in regions immediatelyadjacent to such stopping points, which are referred to herein as stopzones. Stop zones are simply regions adjacent to pick up and drop-offpoints. Stop zones may be characterized or bounded in a number of waysincluding a physical geographic boundary surrounding a pickup ordrop-off point or, for example, as a function of vehicle speeds adjacentto the pick-up and drop-off, as the vehicle slows to stop at thestopping point and accelerates away from it.

Referring to FIGS. 1 and 4, engine stop mode 710 is characterized mostgenerally by bringing engine 145 to a complete stop in response to anengine stop event, typically a door open indication, and restartingengine 145(with zero fuel) in response to an engine start event,typically a door closed indication. Engine stop mode 710 may alsopreferably includes defueling engine 145 as a vehicle enters a stopzone, and refueling engine 145 upon departure from a stop zone. Stopmode 700 also preferably incorporates special control of the EVTpowertrain in conjunction with bringing engine 145 to a complete stop inorder to reduce transient noise and vibrations associated with bringingengine 145 to a complete stop.

Method 700 comprises an engine stop mode 710 of operation for a hybridelectric vehicle having an engine 145 that is operatively andselectively coupled to electric drive motor 143 and transmission 64,comprising the steps of: (1) defueling 800 engine 145 and maintaining900 rotation of engine 145 by rotation of electric drive motor 143 at avehicle speed that is less than a vehicle stop threshold value 715; and(2) decoupling 1000 engine 145 and transmission 64 in response to afirst predetermined vehicle operating condition 720 and stopping 1100the rotation of engine 145. Method 700 and stop mode 710 may beimplemented as a computer control algorithm in a stop mode controller725. Stop mode controller 725 is preferably incorporated into one of thevehicle controller or control modules, such as TCM 17. Engine 145 isoperatively and selectively coupled to electric drive motor 143 andoutput shaft or transmission 64 according to the arrangement describedabove and in FIG. 1. By operatively and selectively, it is simply meantthat both electric drive 143 and transmission 64 may be coupled anddecoupled with respect to providing torque to or receiving torque fromengine 145. Engine 145 defueling 800 while maintaining 900 its rotationis described above as a function of vehicle speed and EBF in conjunctionwith silent mode 110. As shown in FIG. 6, at a vehicle speed that isless than a vehicle stop threshold value 715, engine 145 is defueled andengine output power is zero. For example, engine 145 may be maintainedat an idle speed of approximately 800 rpm while defueled using electricdrive motor 143. The vehicle stop threshold value 715 is also preferablya function of the battery SOC, so that the stop zone is smaller if theEBF is smaller (i.e., a larger deviation from the battery budget). Thestep of decoupling 1000 engine 145 and transmission 64 in response to afirst predetermined vehicle operating condition 720 preferably comprisescommanding a neutral state of the transmission in response to acondition that is indicative of a vehicle stop. This may be any state orcondition associated with the vehicle to which an engine stop may beassociated, or that is generally indicative that an engine stop isdesired, but preferably comprises the opening of the door or doors ofthe vehicle. The opening of the door may be sensed and provided to stopmode controller using conventional switches or other conventional means.If the neutral state is not attained or the not attained before thecommand times out the step of stopping 1100 the rotation of engine 145may be accomplished by simply permitting the frictional forces andmechanical losses to slow engine 145 to a stop. However, if the neutralstate of the transmission has been attained, it is preferred toautomatically apply a torque to oppose the rotation of engine 145 usingelectric drive motor 143 in order to reduce the time required to stopthe rotation of engine 145 and thereby provide a more rapid transitionthrough the natural harmonic frequencies of engine 145, at which itsvibration energy and resultant noise emissions are significantlyincreased (e.g., in an exemplary embodiment, about 350 rpm).

Method 700 also preferably comprises the further steps of: (3)restarting 1200 rotation of the engine in response to a secondpredetermined vehicle operating condition 730 using electric drive motor143; and (4) recoupling 1300 the engine 145 and transmission 64. Secondpredetermined vehicle operating condition 730 may be any state orcondition associated with the vehicle to which an engine restart may beassociated, or that is generally indicative that an engine restart isdesired, but preferably comprises closing the door or doors of thevehicle. The closing of the door may also be sensed and provided to stopmode controller 725 using conventional switches or other conventionalmeans. Restarting 1200 rotation of the engine 145 comprises applying atorque to engine 145 in the direction of the desired rotation usingelectric drive motor 143. Recoupling 1300 the engine 145 andtransmission 64 comprises selecting the operative coupling of the engine143 and transmission 64 and preferably comprises commanding 1400 a rangestate of engine 145 and transmission 64.

Referring to FIGS. 6 and 7, method 700 also preferably comprises thestep of (5) refueling 1500 the engine at a vehicle speed that is greaterthan a vehicle restart threshold value 730. Referring to FIGS.6 and 7,refueling 1400 engine 145 is also a function of vehicle speed and EBF inconjunction with silent mode 110. This step also generally comprisescommanding 1600 a vehicle speed to electric drive motor 143. If thevehicle speed is greater than or equal to vehicle restart thresholdvalue 730, engine 145 is refueled. If the vehicle speed is less thanvehicle restart threshold value 730, engine 145 is not fueled andoperation in the stop mode continues in anticipation of repeating method700 at a subsequent stop. The vehicle restart threshold value 730 isalso preferably a function of the battery SOC, so that the stop zone issmaller if the EBF is smaller (i.e., a larger deviation from the batterybudget). The restart threshold value 725 may be different than the stopthreshold value, but is preferably the same value. It is also preferredthat the battery charge budget does not override the engine stop mode atvehicle stops.

FIG. 9 illustrates preferred embodiment of the general states andtransitions of a vehicle having an EVT powertrain, such as EVTpowertrain 11, comprising electric motor drive 143, engine 145 andtransmission 64 while transitioning into and operating withinstop/restart mode 710. Referring to FIG. 9, block 750 represents a statewherein the vehicle is not in hush mode and the engine is stopped. Atransition 752 is illustrated comprising the operator starting engine145 through normal start button actuation. Following transition 752,block 754 represents a vehicle state wherein the vehicle is not insilent mode 710 (normal operating mode) with engine 145 running,whereupon transition 756, where driver shuts engine off through keyswitch, transition 758, where driver selects HUSH mode and thetransmission is in range, and transition 760, where driver selectssilent mode and transmission is in neutral, are possible. Transition 756simply returns to block 750. Transition 758 results in a staterepresented by block 762, where the vehicle is in silent mode, engine145 is running and transmission 64 is in range. From block 762,transition 764 is possible, wherein the vehicle is in silent mode andvehicle speed is less than the vehicle stop threshold value, such thatengine 145 is defueled with engine 145 rotated by electric dive motor143, vehicle is generally stopped and a first predetermined operatingcondition is detected, such as a door open. Following transition 764,the vehicle state represented by block 766 comprises commanding aneutral state of transmission 64. Referring back to block 762,transition 768 is also possible, wherein the operator deselects silentmode 110 and returns to block 754, whereupon the selections availablefrom the state represented by block 754 are possible. Referring again toblock 762, transition 770 is also possible, wherein, the operatorselects a neutral state of the transmission. Following transition 770,the vehicle state represented by block 772 comprises silent modeoperation with the vehicle stopped, engine running and the transmissionin a neutral state. From the state represented by block 772, transition774, where the operator may selects the range or operatively coupledstate for transmission 64 and thereby returns to block 766 and thetransition choices therefrom, transition 776, wherein the vehicle is insilent mode and vehicle speed is less than the vehicle stop thresholdvalue, such that engine 145 is defueled with engine 145 rotated byelectric dive motor 143, vehicle is generally stopped and a firstpredetermined operating condition is detected, such as a door open, andtransition 778, wherein the operator de-selects the silent mode andreturns to block 754 with its possible transitions. Referring again toblock 766, transition 780, comprising attaining a neutral state oftransmission, and resulting in a state represented by block 782,comprising an active shut down of engine 145, wherein electric drivemotor 143 is used to apply a torque opposite the direction of rotationof engine 145 (wherein the operator still has range selected even thoughneutral state has been automatically commanded and attained ); andtransition 784, comprising not attaining a neutral state of transmissionand the command is timed out waiting for attaining neutral, resulting ina state represented by block 786, comprising a conventional engine stopwith transmission 64 in range. Referring to block 782, transition 788 ispossible, wherein engine 145 is stopped. Referring to block 782,transition 788 is possible, wherein engine 145 is actively stopped(range selected), resulting in a state represented by block 790, whereinengine 145 is stopped. Referring to block 786, transition 792 ispossible, wherein engine 145 is passively stopped (range selected),resulting in a state represented by block 790, wherein engine 145 isstopped and silent mode is still selected. Referring to the staterepresented by block 790, transition 792, comprising occurrence of thesecond predetermined vehicle operation condition (i.e. door closed)while vehicle is in silent mode 110, resulting in the state representedby block 794, wherein range is commanded to the transmission; andtransition 796, comprising occurrence of the second predeterminedvehicle operating condition (i.e. door closed) and the termination ofsilent mode 110 by a mode termination event, resulting in a staterepresented by block 750, and transition choices available from thisblock. Referring to block 794, transition 798, comprising the automaticrestart of engine 145, service brakes are applied, and range is selected(i.e. vehicle was in range before engine 145 was shutdown), resulting ina state represented by block 802, wherein range is automaticallycommanded to transmission 64;and transition 804, comprising theautomatic restart of engine 145, service brakes are not applied, orrange is not selected (i.e. vehicle was in range before engine 145 wasshutdown), or both, resulting in a state represented by block 772, andtransition choices available from this block. Referring to block 802,transition 806 comprises vehicle attaining range, resulting a staterepresented by block 762, and transition choices available from thisblock.

To illustrate method 10, as an example consider the case of an HEVtransit bus, having EVT powertrain 11 and a rechargeable NiMH batterypack, operating in a tunnel with passenger stops. Prior to entering thetunnel, an operator transmits a silent mode initiation request byactuating a silent mode switch that comprises an indicator lamp. Thesilent mode controller evaluates TBAT to determine whetherT_(BAT)≦T_(SMI). If this condition is satisfied, silent mode controllercommands the precharging of the battery and also provides a command tointermittently light the indicator lamp to indicate to the operator thatprecharging is underway. Silent mode controller commands the charging ofthe battery up to the target precharge SOC limit 165, or until the busenters the tunnel and the operator transmits a silent mode activationrequest by actuating a silent mode activation switch which may alsoprovide a lighted feedback indication to the operator. In the tunnel thevehicle is propelled by the electric drive motor according to apredetermined energy budget developed for the target zone or tunnel andthe engine is operated at a minimal level so as to generally onlyprovide the additional propulsion energy necessary when, due to stops,vehicle load, grade or other variables, the electric energy consumed bythe electric drive motor is greater than the budgeted amount as afunction of the distance traveled. This is accomplished by commandingengine power based on the vehicle speed and the ESS budget factorregardless of the output power requirements. If the output powerrequirements exceed the commanded engine power, the ESS supplies thenecessary power to fill in the deficit. If the output power requirementsare less that the commanded engine power, the ESS is charged. Minimizingthe engine power output reduces the noise and exhaust emissions withinthe tunnel. As the bus approaches a passenger pick-up point the vehiclespeed slows to below the vehicle stop threshold value (and the engine isdefueled or commanded to zero fuel) as the bus is slowing for the stop.At the stop, the doors are opened and the stop mode controller sends anengine stop request. Then the engine is stopped, thereby reducing noiseand exhaust emissions at the pick-up point, and passengers board. Afterpassengers are picked up, the vehicle removes the shut down request(typically when the doors close), the engine automatically restarts (butis not fueled) and the drive unit automatically goes into range,allowing the vehicle to move. If the vehicle speed is greater than theengine restart threshold, the engine is refueled. If the speed does notexceed the threshold, the engine is not fueled, in anticipation ofanother stop. If the vehicle maintains a speed that is less than thethreshold using the battery for a period sufficient to exceed thebattery budget, the engine restart threshold value is eventually lowereduntil the vehicle speed exceeds the threshold and the engine is refueledin order to provide propulsion energy to operate the vehicle. After aseries of similar tubes and pick-ups, either the operator commands exitfrom the silent mode, or exit is commanded automatically, and thevehicle returns to normal operation.

It will be apparent to those skilled in the art, that although theinvention has been described in terms of specific and preferredembodiments and examples, modifications and changes may be made to thedisclosed embodiments without departing from the essence of theinvention. Words used herein are words of description rather than oflimitation. It is, therefore, to be understood, that the appended claimsare intended to cover all modifications which naturally flow from theforegoing description and examples.

1. A method of providing a silent mode of operation for a hybridelectric vehicle having a rechargeable energy storage system (ESS),comprising the steps of: (1) transmitting a silent mode initiationrequest to a silent mode controller; (2) comparing an actual value of atleast one state parameter of the ESS that is indicative of theavailability of the ESS for implementing the silent mode to at least onesilent mode initiation limit value associated with the actual value,wherein if the actual value of the at least one state parameter comparedto the associated at least one mode initiation limit value indicatesthat the silent mode is allowed, the method proceeds to step (3), andwherein if the actual value of the at least one state parameterindicates that the silent mode is not allowed, step (2) is repeated solong as the silent mode initiation request is being transmitted; (3)transmitting a silent mode activation request to the silent modecontroller; (4) operating the vehicle in the silent mode using thesilent mode controller, comprising designating an electric drive motoras a primary source of propulsion energy for the vehicle and designatingan engine as a secondary source of the propulsion energy for thevehicle, wherein a modal quantity of energy in the ESS is allocated foruse by the electric drive motor during the silent mode and the engine isused to make up the difference between the modal quantity of energy anda total vehicle propulsion energy requirement during the silent mode;(4A) limiting an output power of the engine while the vehicle is in thesilent mode to a silent mode output power limit that is less than amaximum output power of the engine, and, (5) terminating the silent modein response to the occurrence of a mode termination event.
 2. The methodof claim 1, wherein the step of transmitting a silent mode initiationrequest is selected from the group consisting of: (a) manualtransmitting of the silent mode initiation request by a vehicleoperator, (b) automatic transmitting of the silent mode initiationrequest as a function of an absolute position of the vehicle, and (c)automatic transmitting of the silent mode initiation request as afunction of a relative position of the vehicle to a region in whichsilent mode operation of the vehicle is desired.
 3. The method of claim1, comprising the further step of: (2A) precharging the ESS prior toinitiation of a silent mode.
 4. The method of claim 3, wherein the stepof precharging the ESS comprises precharging the ESS to a state ofcharge (SOC) value that is less than or equal to a target precharge SOClimit.
 5. The method of claim 4, wherein the target precharge SOC limitvalue is in the range of about 60–75 percent.
 6. The method of claim 3,wherein the step of precharging the ESS comprises charging the ESS at amaximum charging power of the vehicle.
 7. The method of claim 1, whereinthe silent mode output power limit of the engine is automaticallycontrolled as a function of a vehicle speed.
 8. The method of claim 7,wherein the maximum silent mode output power limit of the engine is afunction of an ESS budget factor, and wherein as the ESS budget factordecreases, the maximum silent mode output power limit is increased andthe vehicle stop threshold value is decreased.
 9. The method of claim 8,wherein the silent mode output power limit is zero at vehicle speedsthat are less than a vehicle stop threshold value.
 10. The method ofclaim 9, further comprising rotating the engine without fuel at vehiclespeeds that are less than the vehicle stop threshold value.
 11. Themethod of claim 10, further comprising stopping the rotation of theengine in response to an engine stop event.
 12. The method of claim 11,further comprising starting the rotation of the engine in response to anengine start event.
 13. A method of providing a silent mode of operationfor a hybrid electric vehicle having a rechargeable battery, comprisingthe steps of: (1) transmitting a silent mode initiation request to asilent mode controller; (2) comparing a battery temperature to a modeinitiation battery temperature limit value, wherein if the batterytemperature is less than or equal to the mode initiation batterytemperature limit value, the method proceeds to step (3), and wherein ifthe battery temperature is greater than the mode initiation batterytemperature limit value, step (2) is repeated so long as the modeinitiation request is being transmitted; (3) precharging the batteryprior to initiation of a silent mode; (4) transmitting a silent modeactivation request to the silent mode controller; (5) operating thevehicle in the silent mode using the silent mode controller, comprisingdesignating an electric drive motor as a primary source of propulsionenergy for the vehicle and designating an engine as a secondary sourceof the propulsion energy for the vehicle, wherein a modal quantity ofenergy in the battery is allocated for use by the electric drive motorduring the silent mode and the engine is used to make up the differencebetween the modal quantity of energy and a total vehicle propulsionenergy requirement during the silent mode; and (6) terminating thesilent mode in response to the occurrence of a mode termination event.14. The method of claim 13, wherein the step of precharging the batterycomprises precharging the battery to a state of charge (SOC) value thatis less than or equal to a target precharge SOC limit.
 15. The method ofclaim 13, comprising the further step of: (5A) limiting an output powerof the engine while the vehicle is in the silent mode to a maximumsilent mode output power limit that is less than a maximum output powerof the engine.
 16. The method of claim 13, wherein the maximum silentmode output power limit of the engine is a function of an ESS budgetfactor, wherein as the battery budget factor decreases, the maximumsilent mode output power limit is increased.
 17. The method of claim 13,wherein the mode termination event is selected from the group consistingof: (a) manual transmitting of a silent mode termination request by avehicle operator, (b) automatic transmitting of a silent modetermination request as a function of the absolute position of thevehicle, (c) automatic transmitting of a silent mode termination requestas a function of a relative position of the vehicle to a region in whichsilent mode operation of the vehicle is desired a manual modetermination command, (d) reaching a predetermined silent mode elapsedtime limit, (e) reaching a predetermined silent mode elapsed distancelimit, and (f) the battery temperature reaching a predetermined batterytermination limit value, and (g) a battery SOC reaching a predeterminedSOC termination limit value.